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Screw Gearing.

521

gear, with so many threads to the worm that it becomes a wheel.
Fig. 516 shews its application in a Multiple Drill where A A are
tfce drivers, and B B follow on the drill spindles r> D. The wheels
are here equal, and the teeth are inclined at 45 to the axis.

Epicyclic Wheel Trains, like worm gear, produce a high
ratio with few parts. Kinematically they are ordinary trains
where one wheel is the fixed link.

Case L  Fig. 517. Let A and L be in gearv with AL fixed.
If A make a minus rev. with relation to A L, L will have made

- plus revs., because  is the ratio of the train.    Next fix A and

L                                        L

put L out of gear. If now arm A L make one plus rotation two
things have happened : A has made one minus rev. relatively to
A L, and L has made one plus rev. relatively to A. Finally, put
A and L in gear, and give A L one plus rotation . L receives two

one plus rev* due to its connection with A L, and - plus

L

motions

revs, due to the relative minus turn of A

A, and        

I/s revs, 

both relatively to

A

+ =
JL